The separation of liquid components of blood samples, e.g. plasma and serum, is a necessary and important pre-analytical step in clinical diagnostics.
Known methods for performing the above mentioned separation require a considerable amount of manual work and time. The automation of that manual work, both in terms of throughput, workflow and reliability, becomes essential.
An important parameter is the time required for plasma or serum separation during centrifugation. This time could be substantially reduced by centrifugation of the sample tube around its axis of symmetry instead of using the conventional swing bucket method. This is because the length of the motion path followed by cell components of blood sample during centrifugation of the sample container about its symmetry axis is much shorter than in a conventional swing bucket centrifugation of a primary sample tube. When swing bucket centrifugation of a sample tube containing a blood sample is performed the rotation axis is perpendicular to the length axis of the sample tube and the motion path followed by cell components of blood sample during the centrifugation is much longer because the cell components move along the length axis of the sample tube towards the bottom of this tube.
If a primary sample tube is used for example as a sample container for centrifugation around its axis of symmetry, the length of the motion path followed by cell components of blood sample during centrifugation is less than the length of the radius of the primary sample tube, e.g. between 1 and 4 mm.
A problem associated with primary sample tube centrifugation around its axis of symmetry is the maintenance of the separation after centrifugation is stopped. The separated non liquid components are only temporary stuck against the internal wall of the sample tube and will mix again with the liquid component to then slowly sediment at the bottom of the tube.
In U.S. Pat. No. 4,509,941 a sample tube is disclosed comprising a porous material for entrapping blood cells when the tube is centrifuged along its vertical axis. A particularly designed cap helps to keep the porous material in place against the interior wall of the tube. A problem however remains, as the blood cells are not steadily trapped in the porous material. The same document discloses that plasma itself can be used to release the red blood cells from said material. This means that if the separated plasma is not removed quickly, it will be contaminated again by the blood cells.